Process for Hydrosilylation

ABSTRACT

Compounds containing unsaturated carbon-carbon bonds are hydrosilylated with H-silanes or H-siloxanes in the presence of a noble metal catalyst, wherein the water content of the reaction mixture is less than 500 ppm and the noble metal catalyst is supplied as a liquid, and is present in an amount of not more than 50 ppm.

The invention relates to a process for hydrosilylating H-silanes and linear, cyclic or branched H-siloxanes with compounds containing carbon-carbon double bonds or carbon-carbon triple bonds with catalysis with noble metal, wherein, to improve the catalytic activity, the water content of the reaction mixture is not more than 1000 ppm and the catalyst is added to the reaction mixture in liquid form.

In Chemie Ingenieur Technik (1999), 71 (5), 490-493, A. Behr et al. describe the hydrosilylation of alkoxysilane with anhydrous hexachloroplatinic acid. The catalyst used was dried under high vacuum at 260° C. The metering of a solid catalyst has a disadvantageous effect, since this places a high level of technical complexity on the process control and metering precision. The drying method used is additionally uneconomic and impracticable on the industrial scale. The process described also works with very high platinum concentrations, the lowest platinum concentration being 50 ppm. The dried catalyst is a hygroscopic solid, which makes storage and handling difficult in industrial processes.

The European patent EP 0 693 492 B1 describes the hydrosilylation of dimethylchlorosilane (HM2) with allyl methacrylate in the presence of a noble metal catalyst selected from compounds or metals of transition group VIII of the Periodic Table, the water content in the allyl methacrylate being not more than 200 ppm. The allyl methacrylate is dried by means of a molecular sieve or by azeotropic distillation with a water-immiscible solvent. The resulting methacryloyloxypropyldimethylchlorosilane is purified by means of distillation in the presence of a polymerization inhibitor. The process is notable for a low fraction of the undesired α-methylpropionyl-oxypropyldimethylchlorosilane by-product and the reduction in gelling during the final distillation.

In Polymer Preprints (1989), 30 (1), 133-134, L. Lestel discloses the hydrosilylation of polydimethylsiloxane with diallyl-terminated polyethylene oxide in the presence of platinum catalysts selected from the group consisting of dried H2PtCl6 powder, hexachloroplatinic acid dissolved in 1-octanol and 1,2-divinyl-1,1,2,2-tetramethyldisiloxane-platinum complex dissolved in xylene. In the production of membranes consisting of the block copolymers described, bubble formation as a result of hydrogen formed is attributed to the presence of water traces. This is demonstrated with reference to the reaction of pentamethyldisiloxane with water with hydrogen elimination to give the silanol which itself reacts further to give decamethyltetrasiloxane with release of water.

The International patent application WO2004/56907 A2 describes hydrophilic siloxane copolymers prepared by means of hydrosilylation of organopolysiloxanes which have at least one silicon-bonded hydrogen atom per molecule with alkenyl polyethers and subsequent reaction with diisocyanates, with the proviso that the water content of the organopolysiloxane and alkenyl polyether raw materials is less than 2000 ppm. The water content is kept below 2000 ppm owing to the side reaction of the water with the diisocyanates, in order to suppress foam formation in the second reaction step.

The German patent DE 101 33 008 C1 discloses a process for adding silicon-bonded hydrogen onto aliphatic carbon-carbon multiple bonds in the presence of platinum catalysts, in which addition of peracids maintains or enhances the catalytic activity of the platinum catalyst. As a result of their oxidizing action, they can reactivate an inhibited state of the platinum catalyst in the continuous and batchwise hydrosilylation and act as a coactivator or cocatalyst. The disadvantage of this process is the additional addition of an additive in order to maintain the catalytic activity.

It is therefore an object of the present invention to provide a process usable on the industrial scale for hydrosilylating silicon-bonded hydrogen onto carbon-carbon multiple bonds, which enables simple addition of the noble metal catalyst used and ensures a uniformly high or relatively high activity of the catalyst without addition of further assistants.

The object underlying this invention is solved, surprisingly, by keeping the water content of the hydrosilylation composition below 1000 ppm and metering the catalyst in liquid form.

The invention therefore provides a process for hydrosilylating compounds (A) containing carbon-carbon double bonds or carbon-carbon triple bonds with organosilicon compounds having silicon-bonded hydrogen (B) by means of a compound or of a complex of a noble metal of transition group VIII as a catalyst (C), wherein, to improve the catalytic activity, the water content of the reaction mixture is not more than 1000 ppm and the catalyst is added in liquid form to the reaction mixture, with the proviso that the noble metal concentration is not more than 50 ppm, preferably 25 ppm, based on the entire reaction composition.

The water content in the reaction mixture of the process according to the invention is preferably from 0.05 to 500 ppm, more preferably from 0.1 to 100 ppm.

The liquid metering of the catalyst and the maximum water content of 1000 ppm in the reaction mixture give rise to a higher catalytic activity which necessitates a smaller amount of noble metal used. A simultaneous result is shorter plant occupation times. The liquid metering is industrially particularly simple to realize and very precise. This gives rise to safer process control, since fewer variations in the exothermic reaction occur.

The compound (A) used in accordance with the invention may comprise silicon-free organic compounds having aliphatically unsaturated groups, and also organosilicon compounds with aliphatically unsaturated groups.

Examples of organic compounds which can be used as component (A) in the process according to the invention are all types of olefins, such as 1-alkenes, 1-alkynes, vinylcyclohexane, 2,3-dimethyl-1,3-butadiene, 7-methyl-3-methylene-1,6-octadiene, 2-methyl-1,3-butadiene, 1,5-hexadiene, 1,7-octadiene, 4,7-methylene-4,7,8,9-tetrahydroindene, cyclopentene, methylcyclopentadiene, 5-vinyl-2-norbornene, bicyclo[2.2.1]hepta-2,5-diene, 1,3-diisopropenylbenzene, vinyl-containing polybutadiene, 1,4-divinylcyclohexane, 1,3,5-triallylbenzene, 1,3,5-trivinylbenzene, 1,2,4-trivinylcyclohexane, 1,3,5-triisopropenylbenzene, 1,4-divinylbenzene, 3-methyl-1,5-heptadiene, 3-phenyl-1,5-hexadiene, 3-vinyl-1,5-hexadiene and 4,5-dimethyl-4,5-diethyl-1,7-octadiene, diallyl ether, diallylamine, diallyl carbonate, N,N′-diallylurea, triallylamine, tris(2-methylallyl)amine, 2,4,6-triallyloxy-1,3,5-triazine, triallyl-s-triazine-2,4,6(1H,3H,5H)-trione, diallylmalonic esters, allyl alcohols, allyl glycols, allyl glycidyl ether and allylsuccinic anhydride.

In principle, the process according to the invention is also suitable for converting acrylates, for example N,N′-methylenebis(acrylamide), 1,1,1-tris(hydroxymethyl)propane triacrylate, 1,1,1-tris(hydroxymethyl)propane trimethacrylate, tripropylene glycol diacrylate, polyethylene glycol diacrylate, polyethylene glycol dimethacrylate or poly-(propylene glycol) methacrylate.

In addition, aliphatically unsaturated organosilicon compounds can be used as constituent (A) in the process according to the invention.

If organosilicon compounds which have SiC-bonded radicals with aliphatic carbon-carbon multiple bonds are used as constituent (A), they are preferably those composed of units of the formula

R_(a)R¹ _(b)SiO_((4-a-b)/2)  (I),

where

-   R may be the same or different and is an organic radical free of     aliphatic carbon-carbon multiple bonds, -   R¹ may be the same or different and is a monovalent, optionally     substituted, SiC-bonded hydrocarbon radical having an aliphatic     carbon-carbon multiple bond, -   a is 0, 1, 2 or 3 and -   b is 0, 1 or 2,     with the proviso that the sum of a+b is ≦4.

The organosilicon compounds (A) used in accordance with the invention may be either silanes, i.e. compounds of the formula (I) where a+b=4, or siloxanes, i.e. compounds containing units of the formula (I) where a+b≦3.

The R radical includes the monovalent radicals —F, —Cl, —Br, —CN, —SCN, —NCO, alkoxy radicals and SiC-bonded, optionally substituted hydrocarbon radicals which may be interrupted by oxygen atoms or the —C(O)— group.

Examples of R radicals are alkyl radicals, for example the methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl, neopentyl, tert-pentyl radical, hexyl radicals, for example the n-hexyl radical, heptyl radicals, for example the n-heptyl radical, octyl radicals, for example the n-octyl radical and isooctyl radicals, for example the 2,2,4-trimethylpentyl radical, nonyl radicals, for example the n-nonyl radical, decyl radicals, for example the n-decyl radical, dodecyl radicals, for example the n-dodecyl radical, and octadecyl radicals, for example the n-octadecyl radical, cycloalkyl radicals, for example cyclopentyl, cyclohexyl, cycloheptyl and methylcyclohexyl radicals, aryl radicals, for example the phenyl, naphthyl, anthryl and phenanthryl radical, alkaryl radicals, for example o-, m-, p-tolyl radicals, xylyl radicals and ethylphenyl radicals, and aralkyl radicals such as the benzyl radical, and the α- and the β-phenylethyl radical.

Examples of substituted R radicals are haloalkyl radicals such as the 3,3,3-trifluoro-n-propyl radical, the 2,2,2,2′,2′,2′-hexafluoroisopropyl radical and the heptafluoroisopropyl radical, and also haloaryl radicals such as the o-, m- and p-chlorophenyl radical.

The R radical is preferably a monovalent SiC-bonded, optionally substituted hydrocarbon radical which is free of aliphatic carbon-carbon multiple bonds and has from 1 to 18 carbon atoms, more preferably a monovalent SiC-bonded hydrocarbon radical which is free of aliphatic carbon-carbon multiple bonds and has from 1 to 6 carbon atoms, in particular the methyl or phenyl radical.

The R¹ radical may be any groups obtainable by an addition reaction (hydrosilylation) with an SiH-functional compound.

If the R¹ radical is SiC-bonded, substituted hydrocarbon radicals, preferred substituents are halogen atoms, cyano radicals, alkoxy groups and siloxy groups.

The R¹ radical is preferably alkenyl and alkynyl groups having from 2 to 16 carbon atoms, such as vinyl, allyl, methallyl, 1-propenyl, 5-hexenyl, ethynyl, butadienyl, hexadienyl, cyclopentenyl, cyclopentadienyl, cyclohexenyl, vinylcyclohexylethyl, divinylcyclohexylethyl, norbornenyl, vinylphenyl and styryl radicals, particular preference being given to vinyl, allyl and hexenyl radicals.

Preferred components (A) are all terminal olefins and all allylic, vinylic and alkynic systems, particular preference being given to allylic systems.

The organosilicon compounds (B) used may be all hydrogen-functional organosilicon compounds which have also been used before in hydrosilylation reactions.

The organosilicon compounds (B) having Si-bonded hydrogen atoms used are preferably those which contain units of the formula

R² _(c)H_(d)SiO_((4-c-d)/2)  (II)

where R² may be the same or different and is as defined above for R, c is 0, 1, 2 or 3 and d is 0, 1 or 2, with the proviso that the sum of c+d is ≦4 and at least one Si-bonded hydrogen atom is present per molecule.

The R² radicals are preferably selected from the group comprising the monohydric radicals —F, —Cl, —Br, —CN, —SCN, —NCO and SiC-bonded, optionally substituted hydrocarbon radicals, for example alkyl radicals, for example the methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl, neopentyl, tert-pentyl radical, hexyl radicals, for example the n-hexyl radical, heptyl radicals, for example the n-heptyl radical, octyl radicals, for example the n-octyl radical and isooctyl radicals, for example the 2,2,4-trimethylpentyl radical, nonyl radicals, for example the n-nonyl radical, decyl radicals, for example the n-decyl radical, dodecyl radicals, for example the n-dodecyl radical, and octadecyl radicals, for example the n-octadecyl radical, cycloalkyl radicals, for example cyclopentyl, cyclohexyl, cycloheptyl and methylcyclohexyl radicals, aryl radicals, for example the phenyl, naphthyl, anthryl and phenanthryl radical, alkaryl radicals, for example o-, m-, p-tolyl radicals, xylyl radicals and ethylphenyl radicals, and aralkyl radicals such as the benzyl radical, and the α- and the β-phenylethyl radical.

The organosilicon compounds (B) used in accordance with the invention may either be silanes, i.e. compounds of the formula (II) where c+d=4, or siloxanes, i.e. compounds containing units of the formula (II) where c+d≦3. The organosilicon compounds used in accordance with the invention are preferably organopolysiloxanes, especially those which consist of units of the formula (II).

The organosilicon compound (B) used in accordance with the invention preferably contains Si-bonded hydrogen in the range from 0.02 to 1.7 percent by weight, based on the total weight of the organosilicon compound (B).

The molecular weight of constituent (B) in the case of siloxane may vary within wide limits, for instance between 10² and 10⁶ g/mol. For example, constituent (B) may be a relatively low molecular weight SiH-functional oligosiloxane such as tetramethyldisiloxane, but also a high molecular weight polydimethylsiloxane possessing pendant or terminal SiH groups or a silicone resin having SiH groups. The structure of the molecules forming constituent (B) is also not fixed; in particular, the structure of a relatively high molecular weight, i.e. oligomeric or polymeric, SiH-containing siloxane may be linear, cyclic, branched or else resin-like, network-like.

In the process according to the invention, constituent (B) is preferably used in such an amount that the molar ratio of aliphatically unsaturated groups of constituent (A) to SiH groups of constituent (B) is between 0.1 and 20 and, for siloxanes, preferably between 1.0 and 5.0.

The components (A) and (B) used in accordance with the invention are commercial products or preparable by processes common in chemistry.

In the process according to the invention, the component (C) used may be all catalysts which have also been used before for the addition of Si-bonded hydrogen to aliphatically unsaturated compounds. Examples of such catalysts are compounds or complexes of the group of the noble metals comprising platinum, ruthenium, iridium, rhodium and palladium, for example platinum halides, platinum-olefin complexes, platinum-alcohol complexes, platinum-alkoxide complexes, platinum-ether complexes, platinum-aldehyde complexes, platinum-ketone complexes, including reaction products of H₂PtCl₆.6H₂O and cyclohexanone, platinum-vinylsiloxane complexes, especially platinum-divinyltetramethyldisiloxane complexes with or without a content of detectable inorganically bonded halogen, bis(γ-picoline)platinum dichloride, trimethylenedipyridineplatinum dichloride, dicyclopentadieneplatinum dichloride, dimethylsulfoxyethyleneplatinum(II) dichloride and reaction products of platinum tetrachloride with olefin and primary amine or secondary amine or primary and secondary amine, for example the reaction product of platinum tetrachloride dissolved in 1-octene with sec-butylamine. In a further preferred embodiment of the process according to the invention, complexes of iridium with cyclooctadienes, for example μ-dichlorobis(cyclooctadiene)diiridium(I), are used.

The catalyst (C) is preferably compounds or complexes of platinum, preferably platinum chlorides and platinum complexes, especially platinum-olefin complexes and more preferably platinum-divinyltetramethyldisiloxane complexes.

In the process according to the invention, catalyst (C) is used in amounts of from 1 to 50 ppm by weight, calculated as elemental noble metal and based on the total weight of component (A) and (B) present in the compositions. Preference is given to using from 5 to 25 ppm by weight.

In a likewise preferred embodiment, silanes of the general formula (III)

R³ _(e)H_(f)Si  (III)

are reacted, where R³ may be the same or different and is as defined above for R, e is 1, 2 or 3 and f is 1, 2 or 3, with the proviso that the sum of e+f=4.

Examples of R³ radicals are in particular —F, —Cl, —Br, —CN, —SCN, —NCO and the SiC-bonded, optionally substituted alkyl and aryl radicals specified for the R radical, and also halogen-substituted aryl radicals, preference being given to methyl, propyl, phenyl and halogenated phenyl radicals and particular preference to the methyl radical and halogenated phenyl radicals.

The process according to the invention can be carried out in the presence or absence of organic solvent (D).

Examples of organic solvents (D) are all solvents which have also been usable before in hydrosilylation reactions, such as toluene, xylene, isopropanol, acetone, isophorone and glycols.

If organic solvents (D) are used, they are preferably toluene, isopropanol and glycols, and more preferably toluene.

If organic solvents (D) are used in the process according to the invention, the amounts are preferably from 5 to 60% by weight, more preferably from 5 to 40% by weight, based in each case on the total weight of the reaction mixture.

In the process according to the invention, apart from components (A) to (D), it is also possible to use all further substances (E) which have also been used before in hydrosilylation reactions.

In the process according to the invention, preference is given to not using any further substances in addition to components (A) to (E).

The components (A) to (E) used in accordance with the invention may each be a single type of such a component or a mixture of at least two different types of such a component.

In the process according to the invention, the components used may be mixed with one another by any known processes. In the process according to the invention, preference is given to either initially charging all reagents apart from catalyst (C) and then starting the reaction by adding the catalyst, or to initially charging all reagents apart from the Si—H— containing compounds (B) and then metering in the Si—H— containing compounds.

The process according to the invention can be carried out continuously or batchwise.

In the process according to the invention, Si-bonded hydrogen can be added onto aliphatic multiple bonds under the same conditions as in the hydrosilylation reactions known to date.

The temperatures are preferably from 20 to 200° C., more preferably from 60 to 140° C., and the pressure from 1 to 20 bar. However, it is also possible to employ higher or lower temperatures and pressures.

The organosilicon compounds prepared in the process according to the invention may be used for all purposes for which modified organosilicon compounds have also been used before.

The process according to the invention has the advantage that a significant catalyst reduction can be achieved, since the catalytic activity of the original catalyst can be significantly increased and prolonged.

In addition, the process according to the invention has the advantage that a catalyst reduction can also achieve secondary effects, such as improved color qualities and lower proportion of toxic heavy metals in the hydrosilylation product, especially in the case of polysiloxanes.

The water content of not more than 1000 ppm in the reaction mixture can be achieved by the use of starting compounds with correspondingly low water contents or the pretreatment of the starting compounds used and of the catalyst, for example with a suitable desiccant.

Examples of suitable desiccants are calcium chloride, magnesium sulfate, sodium sulfate, metals or molecular sieve. Unsuitable desiccants for the H-siloxanes are, for example, potassium hydroxide, sodium hydroxide or acidic alumina, which lead to the reaction with SiH or equilibration reactions. In the case of H-containing chlorosilanes, particular preference is given to the preliminary blending of the catalyst in H-free chlorosilane as a desiccant, for example silicon tetrachloride.

The time up to the exothermic temperature jump after the start of the hydrosilylation reaction can be considered as a measure of the catalytic activity. For this purpose, the SiH-containing and olefinic component are mixed and, after addition of the catalyst, the temperature increase which sets in is monitored.

A further measure of the catalytic activity in the case of inhomogeneous starting mixtures is the time until, for example, a clear mixture is present in the case of polyether/silicone mixtures.

EXAMPLES 1.) Chlorosilane A) Comparative Example Without “Drying” (Noninventive)

A 100 ml glass flask is initially charged with 29 g (0.13 mol) of hexadecene at room temperature which are mixed with 19.0 g (0.14 mol) of trichlorosilane. The reaction mixture is admixed with 0.05 g of a platinum catalyst solution (4% by weight of platinum) in dodecene. After approx. 5 minutes, the reaction mixture exhibits a high temperature rise and attains the temperature maximum after 12 minutes. The reaction is complete after 15 minutes.

B) Inventive Example

Drying: 10 g of a platinum catalyst solution are admixed with 2% by weight of tetrachlorosilane at room temperature and stirred for 15 minutes.

A 100 ml glass flask is initially charged with 29 g (0.13 mol) of hexadecene at room temperature which are mixed with 19.0 g (0.14 mol) of trichlorosilane. The reaction mixture is admixed with 0.05 g of a dried platinum catalyst solution (4% by weight of platinum) in dodecene. After approx. 3 minutes, the reaction mixture exhibits a high temperature rise and attains the temperature maximum after 8 minutes. The reaction is complete after 10 minutes.

2.) Glycol-Functional Silicone Oil A) Comparative Example Hydrosilylation with >1000 ppm of H2O in the Reaction Mixture (Noninventive)

800 g of an α,ω-dihydropolydimethylsiloxane with 0.055% by weight of Si-bonded hydrogen and a water content of 55 ppm by weight are mixed with 1407 g of an allyl alcohol ethoxylate/propyloxylate of the formula

H₂C═CH—CH₂—(OCH₂CH₂)_(a)[OCH₂CH(CH₃)]_(b)—OH,

with an a:b ratio=1.0, a water content of 1619 ppm by weight and an iodine number of 14.3 (the iodine number refers to the number which specifies the amount of iodine in grams consumed in the addition to the aliphatic multiple bond per 100 grams of material to be analyzed used).

The reaction mixture is heated to 95° C. and admixed at reaction temperature with 2.20 g of a 1.25% solution of hexachloroplatinic acid in dimethoxyethane.

The reaction mixture heats up by 6° C. and is homogeneous 15 minutes after the start of the reaction.

B) Inventive Example

The preceding example is repeated except, for comparison, by using a polyether which has been dried beforehand under high vacuum at 100° C. for 2 hours. As a result, the water content of the polyether is 127 ppm by weight.

The reaction mixture heats up by 8° C. and is homogeneous as early as 12 min after the start of the reaction.

3.) Carbinol-Functional Silicone Oil A) Comparative Example Hydrosilylation with >1000 ppm of H2O in the Reaction Mixture (Noninventive)

100 g of allyl alcohol, 113 ml of toluene and 1 g of anhydrous sodium carbonate are initially charged in a three-neck flask and heated to 90° C. After addition of 2.0 ml of the platinum catalyst solution (1.25% solution of hexachloroplatinic acid in dimethoxyethane), 585 g of an α,ω-dihydropolydimethylsiloxane with 0.22% by weight of Si-bonded hydrogen are metered in continuously, so that the reaction temperature is from 90 to 110° C. The metering time is 1.5 hours. The reaction mixture is kept at 105° C. for a further hour and then cooled to room temperature. The hydrogen number is determined as a measure of the reaction progress. The hydrogen number is 55 (target value <10), and so another 2.0 ml of the catalyst solution (1.25% solution of hexachloroplatinic acid in dimethoxyethane) are added and the reaction mixture is heated to 105° C. for a further 1.5 hours. The hydrogen number of the brown reaction solution is 8 and the water content 1285 ppm. On a rotary evaporator, the low boilers are distilled off at 112° C./0.5 hour/vacuum <1 mbar. The residue is filtered to obtain a carbinol-functional silicone oil with the following properties: Hazen color number (DIN ISO 6271): 54; water content: 794 ppm.

B) Inventive Example

The preceding example is repeated except, for comparison, by using an α,ω-dihydropolydimethylsiloxane which has been baked out beforehand under high vacuum at 90° C. for 1 hour. There is no need for a second addition of the platinum catalyst solution, since the first value of the hydrogen number measurement is 9. The resulting carbinol-functional silicone oil has the following properties: Hazen color number (DIN ISO 6271): 6; water content: 390 ppm. 

1.-12. (canceled)
 13. A process for hydrosilylating compounds (A) containing carbon-carbon double bonds or carbon-carbon triple bonds with organosilicon compounds (B) having silicon-bonded hydrogen by catalysis with a compound or complex of a noble metal of transition group VIII as a catalyst (C), comprising desiccating starting materials with a desiccant selected from the group consisting of calcium chloride, magnesium sulfate, sodium sulfate, metals, molecular sieves or H-free chlorosilanes, such that the water content of the reaction mixture is not more than 500 ppm and the catalyst is added in liquid form to the reaction mixture, with the proviso that the noble metal concentration is not more than 50 ppm based on the entire reaction composition.
 14. The process of claim 13, wherein the noble metal catalyst concentration is from 5 to 25 ppm based on the entire reaction composition.
 15. The process of claim 13, wherein the water content of the reaction mixture is not more than 100 ppm.
 16. The process of claim 14, wherein the water content of the reaction mixture is not more than 100 ppm.
 17. The process of claim 13, wherein the catalyst (C) comprises one or more compounds or complexes of a noble metal selected from the group consisting of platinum, ruthenium, iridium, rhodium and palladium.
 18. The process of claim 13, wherein the catalyst (C) used comprises at least one platinum-olefin complex or platinum-divinyltetramethyldisiloxane complex.
 19. The process of claim 13, wherein the process is carried out at a temperature of from 60 to 140° C.
 20. The process of claim 13, wherein the process is carried out at a pressure of from 1 to 20 bar.
 21. The process of claim 13, wherein organosilicon compounds with silicon-bonded hydrogen (B) comprise compounds containing units of the formula (II) R² _(c)H_(d)SiO_((4-c-d)/2)  (II) where R² are identical or different monovalent radicals selected from the group consisting of —F, —Cl, —Br, —CN, —SCN, —NCO, alkoxy radicals, and SiC-bonded, substituted or unsubstituted hydrocarbon radicals optionally interrupted by oxygen atoms or a —C(O)— group, c is 0, 1, 2 or 3 and d is 0, 1 or 2, with the proviso that the sum of c+d is ≦ and at least one Si-bonded hydrogen atom per molecule is present.
 22. The process of claim 13, wherein organosilicon compounds having silicon-bonded hydrogen (B) comprise silanes of the formula (III) R³ _(e)H_(f)Si  (III) where R³ are identical or different monovalent radicals selected from the group consisting of —F, —Cl, —Br, —CN, —SCN, —NCO, alkoxy radicals, and Si—C-bonded, substituted or unsubstituted hydrocarbon radicals optionally interrupted by oxygen atoms or the —C(O)— group, e is 1, 2 or 3 and f is 1, 2 or 3, with the proviso that the sum of e+f=4.
 23. The process of claim 13, wherein the desiccant comprises silicon tetrachloride.
 24. A process for hydrosilylating compounds (A) containing carbon-carbon double bonds or carbon-carbon triple bonds with organosilicon compounds (B) having silicon-bonded hydrogen by catalysis with a compound or complex of a noble metal of transition group VIII as a catalyst (C), comprising desiccating starting materials (A) and/or (B), and desiccating the such that the water content of the reaction mixture is not more than 500 ppm and the catalyst is added in liquid form to the reaction mixture, with the proviso that the noble metal concentration is not more than 50 ppm based on the entire reaction composition. 